During the peak of the last ice age, one-third of the Earth's
land surface was covered by thick sheets of ice. Their high albedo
reflected a great deal of sunlight out into space, which cooled Earth and
allowed the ice
sheets to grow. (See our Ice
Ages web
page.) Ice sheets give birth to icebergs. This process is known as calving.
Most bergs are calved from ice sheets off the western coast of Greenland
and
Antarctica. Icebergs are found in both the Arctic and Antarctic regions.
The bergs from these two areas differ, however, in form and size.

So what criteria must a chunk of ice meet to officially
be called an iceberg? By definition, icebergs are at least seventeen feet
proud of the water and fifty feet long. Anything smaller is called
a growler
or bergy
bits.
One of the biggest Greenland bergs ever reported by the Coast Guard was
550
feet above the sea. Icebergs in the Arctic regions are formed from mountain
glaciers fed by the Greenland ice sheets and are high and narrow, with above-water
shapes resembling towers; these are called
castle
bergs.
Large tabular icebergs are found at the ice shelves of Antarctica. One large
tabular Antarctic iceberg in 1987 was reported to be 100 miles long,
25 miles wide, and 750 feet thick.

Castle or pinnacle bergs (like the one pictured
above) are found only in the Arctic regions. Tabular bergs (like the one
pictured below) are found in the Antarctic regions.

Have you ever heard the phrase, "it
was just the tip of the iceberg?" It's a phrase or metaphor that figuratively
means that what you see is not all there is. This is literally true of an
iceberg. The higher the iceberg rises above the ocean surface, the deeper
its base projects into the water. The exact depth of immersion depends on
the difference in density between the ice and the seawater, but it will
be three to nine times the iceberg's height (WOW!) above the water line.